1. Field of the Invention
The invention proceeds from a capacitive voltage transformer for a metal-enclosed, gas-filled high-voltage system according to the preamble of patent claim 1. Such a voltage transformer contains a cylindrical capacitor having two coaxially arranged, electrically conducting cylinders of which an internally arranged cylinder is at a high voltage potential, and an externally arranged cylinder is inserted in an electrically insulated fashion into the metal enclosure. Such a voltage divider can be accommodated in a space-saving fashion in the metal enclosure and can be combined in a simple way with a current transformer.
2. Discussion of Background
In this case, the invention refers to a prior art such as emerges, for example, from EP-A2-522 303. A combined current and voltage transformer, published in this prior art, for a metal-enclosed, gas-filled high-voltage system has a tubularly constructed metal-enclosed section, a conductor guided along the tube axis, and a hollow cylindrical measuring electrode, which is inserted into the metal enclosure in an insulating fashion and concentrically surrounds the conductor, which preferably carries the phase current. The measuring electrode forms with the conductor a cylindrical capacitor which decouples the electric field emanating from the conductor and corresponding to the high voltage supplied, and acts as an overvoltage capacitor of a capacitive voltage divider.
Depending on the measurement task, it is necessary for the voltage values transformed by this apparatus to have a more or less high level of accuracy. The gain influencing the accuracy of the transformed voltage values depends on the temperature of the cylindrical capacitor acting as voltage sensor, as well as on the density of the insulating gas present in the system. The gas density and the temperature of the measuring electrode, acting as external cylinder, of the cylindrical capacitor can be measured with a low outlay, and be taken into account in a simple way when correcting the ratio accuracy. By contrast, there is a problem in measuring the temperature, likewise featuring in the ratio accuracy, of the conductor, which is at a high voltage potential and acting as the internal cylinder of the cylindrical capacitor.